1. Field of Invention
The present invention relates in general to a control device for controlling an internal combustion engine, and more particularly to an intake valve control device of an internal combustion engines, which comprise a working angle varying mechanism for varying the working angle of an intake valve and an operation phase varying mechanism for varying an operation phase of the intake valve.
2. Description of Related Art
Hitherto, various types of intake valve control devices have been proposed and put into practical use in the field of automotive internal combustion engines. One of such types is shown in an instruction manual of Toyota car (Celica) issued on September 1999 from Toyota Jidosha Kabushiki Kaisha, which comprises a working angle varying mechanism which varies the working angle of each intake valve by switching high and low speed cams in accordance with a hydraulic pressure led from an oil pump driven by the engine crankshaft and an operation phase varying mechanism which varies the operation phase of the intake valve by changing a relative angular position between a cam pulley (rotation member) synchronously rotated with the crankshaft and an intake valve cam shaft.
It is now to be noted that the term xe2x80x9cworking anglexe2x80x9d used in the description corresponds to the open period of the corresponding valve or valves and is represented by an angle range (viz., crank angle) of the engine crankshaft, and the term xe2x80x9coperation phasexe2x80x9d used in the description corresponds to the operation timing of the corresponding valve or valves relative to the engine crankshaft.
In general, in a middle-load operation range of the engine, improvement in fuel consumption and that in exhaust performance are achieved by providing a satisfied valve overlap between the intake and exhaust valves. With this satisfied valve overlap, the internal EGR is increased and pumping loss is reduced. While, in a very-low-speed (or very-low-load) operation range of the engine, such as, a range provided when the engine is under idling, the valve overlap should be reduced to minimize the residual gas for achieving a stable combustion of the engine. Accordingly, in case of rapid deceleration of engine speed from the middle-load operation range to the very-low-load operation range, it is inevitably necessary to speedily reduce the valve overlap. However, in known intake valve control devices like the above-mentioned one, when, like in the low-speed operation range of the engine, the hydraulic pressure led from the oil pump is low, quick switching of the working angle by the working angle varying mechanism is difficult. Thus, considering the rapid deceleration of the engine speed which takes place upon sharp braking of the associated motor vehicle, the valve overlap can not be so increased.
Accordingly, an object of the present invention to provide an intake valve control device of an internal combustion engine, which can assuredly and speedily reduce the valve overlap even in a rapid deceleration of the engine speed.
Another object of the present invention is to provide an intake valve control device of an internal combustion engine, which can provide in a given operation range a satisfied valve overlap which has a high responsiveness.
According to a first aspect of the present invention, there is provided an intake valve control device of an internal combustion engine having intake and exhaust valves. The control device comprises a first mechanism which varies a working angle of the intake valve; a second mechanism which varies an operation phase of the intake valve; and a control unit which controls both the first and second mechanisms in accordance with an operation condition of the engine, the control unit being configured to carry out controlling variation in the open timing of the intake valve effected by the first mechanism to be larger than variation in the open timing of the intake valve effected by the second mechanism.
According to a second aspect of the present invention, there is provided a method of controlling an internal combustion engine which has intake and exhaust valves, a first mechanism which varies a working angle of the intake valve and a second mechanism which varies an operation phase of the intake valve. The method comprises controlling variation in the open timing of the intake valve effected by the first mechanism to be larger than variation in the open timing of the intake valve effected by the second mechanism.